Question

I have a 1-1 column relation between two tables, item and log

For each item, there’s a log which stores whether item has been processed or not. This is identified by log.itemId being equal to item.id. log.status tells if the processing is in progress, or has finished (-1 being pending, 1 being finished).

Before processing starts, there’s no row in the log table for the corresponding item in item table.

I’m trying simply to get the rows from item where either there’s no corresponding row in log (meaning processing hasn’t started) or where status is not 1 (meaning its pending).

I’m going crazy trying to figure this out, this is my query:

SELECT 
    item.id
FROM item, log
WHERE log.itemId != item.id
OR (log.itemId = item.id AND log.status !='1')
ORDER BY item.id ASC LIMIT 1

However this returns an empty result.

What am I doing wrong?

Answer 1

Try this:

SELECT 
  item.id
FROM
  item left join log on (log.itemId = item.id)
WHERE
  log.itemId is null
  OR log.status !='1'
ORDER BY item.id LIMIT 1